fix: qbt reuse existing torrent

src/Chaptarr.Core.Test/Download/QBittorrentDuplicateHandlingFixture.cs

@@ -43,12 +43,19 @@ private class TestProxy : IQBittorrentProxy
 
             public QBittorrentPreferences GetConfig(QBittorrentSettings settings) => new QBittorrentPreferences { DhtEnabled = true };
 
-            public List<QBittorrentTorrent> GetTorrents(QBittorrentSettings settings, string category = null) => throw new NotImplementedException();
+            public Dictionary<string, List<string>> HashesByCategory { get; } = new(StringComparer.OrdinalIgnoreCase);
+            public bool TorrentLoaded { get; set; }
+
+            public List<QBittorrentTorrent> GetTorrents(QBittorrentSettings settings, string category = null)
+            {
+                var hashes = category != null && HashesByCategory.TryGetValue(category, out var found) ? found : new List<string>();
+                return hashes.ConvertAll(hash => new QBittorrentTorrent { Hash = hash });
+            }
 
             public bool IsTorrentLoaded(string hash, QBittorrentSettings settings)
             {
                 LoadedHashes.Add(hash);
-                return false;
+                return TorrentLoaded;
             }
 
             public QBittorrentTorrentProperties GetTorrentProperties(string hash, QBittorrentSettings settings) => throw new NotImplementedException();
@@ -242,11 +249,84 @@ public void should_surface_non_conflict_errors_unchanged()
             Assert.Multiple(() =>
             {
                 Assert.That(exception, Is.SameAs(original));
+                Assert.That(proxy.Labels, Is.Empty);
+            });
+        }
+
+        [Test]
+        public void should_continue_with_existing_torrent_already_in_a_chaptarr_category()
+        {
+            var proxy = new TestProxy { AddException = new DownloadClientException("qBittorrent rejected the torrent add request (response: Fails.).") };
+            proxy.HashesByCategory["ebooks"] = new List<string> { "abcdef1234" };
+            var client = CreateClient(proxy);
+
+            var result = client.AddTorrentFile(CreateRemoteBook(), "ABCDEF1234");
+
+            Assert.Multiple(() =>
+            {
+                Assert.That(result, Is.EqualTo("ABCDEF1234"));
                 Assert.That(proxy.LoadedHashes, Is.Empty);
                 Assert.That(proxy.Labels, Is.Empty);
             });
         }
 
+        [Test]
+        public void should_move_existing_torrent_back_from_post_import_category()
+        {
+            var proxy = new TestProxy { AddException = new DownloadClientException("qBittorrent rejected the torrent add request (response: Fails.).") };
+            proxy.HashesByCategory["ebooks-imported"] = new List<string> { "abcdef1234" };
+            var client = CreateClient(proxy);
+
+            client.AddMagnet(CreateRemoteBook(), "ABCDEF1234");
+
+            Assert.That(proxy.Labels, Is.EqualTo(new[] { ("abcdef1234", "ebooks") }));
+        }
+
+        [Test]
+        public void should_reject_without_adopting_when_existing_torrent_is_outside_chaptarr_categories()
+        {
+            var proxy = new TestProxy
+            {
+                AddException = new DownloadClientException("qBittorrent rejected the torrent add request (response: Fails.)."),
+                TorrentLoaded = true
+            };
+            var client = CreateClient(proxy);
+
+            var exception = Assert.Throws<DownloadClientRejectedReleaseException>(() => client.AddTorrentFile(CreateRemoteBook(), "ABCDEF1234"));
+
+            Assert.Multiple(() =>
+            {
+                Assert.That(exception.Message, Is.EqualTo("qBittorrent already has this torrent outside Chaptarr's categories"));
+                Assert.That(proxy.Labels, Is.Empty);
+            });
+        }
+
+        private static TestQBittorrent CreateClient(TestProxy proxy)
+        {
+            return new TestQBittorrent(new TestProxySelector(proxy, new Version(2, 11, 0)), new CacheManager(), LogManager.GetCurrentClassLogger())
+            {
+                Definition = new DownloadClientDefinition
+                {
+                    Name = "qBittorrent",
+                    Settings = new QBittorrentSettings
+                    {
+                        EbookCategory = "ebooks",
+                        AudiobookCategory = "audiobooks",
+                        EbookImportedCategory = "ebooks-imported"
+                    }
+                }
+            };
+        }
+
+        private static RemoteBook CreateRemoteBook()
+        {
+            return new RemoteBook
+            {
+                Books = new List<Book> { new Book { MediaType = BookMediaType.Ebook } },
+                Release = new TorrentInfo()
+            };
+        }
+
         private static DownloadClientException ConflictException()
         {
             var request = new HttpRequest("http://localhost/api/v2/torrents/add");

src/NzbDrone.Core/Download/Clients/QBittorrent/QBittorrent.cs

@@ -91,6 +91,57 @@ public bool ShouldPreserveItemAfterImport(DownloadClientItem downloadClientItem)
                 Settings.EbookImportedCategory);
         }
 
+        private bool TryAdoptExistingTorrent(RemoteBook remoteBook, string hash, string category, DownloadClientException addException)
+        {
+            if (hash.IsNullOrWhiteSpace())
+            {
+                return false;
+            }
+
+            string existingCategory;
+            bool existsElsewhere;
+
+            try
+            {
+                existingCategory = new[] { Settings.AudiobookCategory, Settings.EbookCategory, Settings.AudiobookImportedCategory, Settings.EbookImportedCategory }
+                    .Where(c => c.IsNotNullOrWhiteSpace())
+                    .Distinct(StringComparer.InvariantCultureIgnoreCase)
+                    .FirstOrDefault(c => Proxy.GetTorrents(Settings, c).Any(t => hash.Equals(t.Hash, StringComparison.OrdinalIgnoreCase)));
+
+                existsElsewhere = existingCategory == null && Proxy.IsTorrentLoaded(hash.ToLower(), Settings);
+            }
+            catch (Exception ex)
+            {
+                _logger.Debug(ex, "Unable to check whether torrent {0} already exists in qBittorrent", hash);
+                return false;
+            }
+
+            if (existsElsewhere)
+            {
+                throw new DownloadClientRejectedReleaseException(remoteBook.Release, "qBittorrent already has this torrent outside Chaptarr's categories", addException);
+            }
+
+            if (existingCategory == null)
+            {
+                return false;
+            }
+
+            if (category.IsNotNullOrWhiteSpace() && !category.Equals(existingCategory, StringComparison.InvariantCultureIgnoreCase))
+            {
+                try
+                {
+                    Proxy.SetTorrentLabel(hash.ToLower(), category, Settings);
+                }
+                catch (DownloadClientException ex)
+                {
+                    _logger.Warn(ex, "Failed to move existing torrent {0} from category \"{1}\" to \"{2}\" in qBittorrent.", hash, existingCategory, category);
+                }
+            }
+
+            _logger.Info("qBittorrent already has torrent {0} in Chaptarr category \"{1}\"; continuing with the existing download instead of failing the grab", hash, existingCategory);
+            return true;
+        }
+
         protected override string AddFromMagnetLink(RemoteBook remoteBook, string hash, string magnetLink)
         {
             if (!Proxy.GetConfig(Settings).DhtEnabled && !magnetLink.Contains("&tr="))
@@ -113,6 +164,13 @@ protected override string AddFromMagnetLink(RemoteBook remoteBook, string hash,
             {
                 throw new DownloadClientRejectedReleaseException(remoteBook.Release, "qBittorrent rejected the magnet link due to a conflict", ex);
             }
+            catch (DownloadClientException ex)
+            {
+                if (!TryAdoptExistingTorrent(remoteBook, hash, category, ex))
+                {
+                    throw;
+                }
+            }
 
             if ((!addHasSetShareLimits && setShareLimits) || moveToTop || forceStart)
             {
@@ -178,6 +236,13 @@ protected override string AddFromTorrentFile(RemoteBook remoteBook, string hash,
             {
                 throw new DownloadClientRejectedReleaseException(remoteBook.Release, "qBittorrent rejected the torrent file due to a conflict", ex);
             }
+            catch (DownloadClientException ex)
+            {
+                if (!TryAdoptExistingTorrent(remoteBook, hash, category, ex))
+                {
+                    throw;
+                }
+            }
 
             if ((!addHasSetShareLimits && setShareLimits) || moveToTop || forceStart)
             {